Tissue factor (TF), also called thromboplastin, factor III or CD142 is a protein present in subendothelial tissue, platelets, and leukocytes necessary for the initiation of thrombin formation from the zymogen prothrombin. Thrombin formation ultimately leads to the coagulation of blood. Tissue factor enables cells to initiate the blood coagulation cascades, and it functions as the high-affinity receptor for the coagulation factor VII. The resulting complex provides a catalytic event that is responsible for initiation of the coagulation protease cascades by specific limited proteolysis. Unlike the other cofactors of these protease cascades, which circulate as nonfunctional precursors, this factor is a potent initiator that is fully functional when expressed on cell surfaces.
Tissue factor is the cell surface receptor for the serine protease factor VIIa (FVIIa). Binding of FVIIa to tissue factor has been found to start signaling processes inside the cell said signaling function playing a role in angiogenesis. Whereas angiogenesis is a normal process in growth and development, as well as in wound healing it is also a fundamental step in the transition of tumors from a dormant state to a malignant state: when cancer cells gain the ability to produce proteins that participate in angiogenesis, so called angiogenic growth factors, these proteins are released by the tumor into nearby tissues, and stimulate new blood vessels to sprout from existing healthy blood vessels toward and into the tumor. Once new blood vessels enter the tumor it can rapidly expand its size and invade local tissue and organs. Through the new blood vessels cancer cells may further escape into the circulation and lodge in other organs to form new tumors (metastases).
Further TF plays a role in inflammation. The role of TF is assumed to be mediated by blood coagulation (A. J. Chu: “Tissue factor mediates inflammation” in Archives of biochemistry and biophysics, 2005, vol. 440, No. 2, pp. 123-132). Accordingly, the inhibition of TF e.g. by monoclonal anti-TF antibodies is of significance in interrupting the coagulation-inflammation cycle in contribution to not only anti-inflammation but also to vascular diseases.
TF expression is observed in many types of cancer and is associated with more aggressive disease. Furthermore, human TF also exist in a soluble alternatively-spliced form, asHTF. It has recently been found that asHTF promotes tumor growth (Hobbs et al. 2007 Thrombosis Res. 120(2) S13-S21).
Antibodies binding to TF have been disclosed in the prior art:
WO98/40408 discloses antibodies that can bind native human TF, either alone or present in a TF:VIIa complex, effectively preventing factor X binding to TF or that complex, and thereby reducing blood coagulation. It is disclosed that the antibodies may be used to alleviate thromboses following an invasive medical procedure such as arterial or cardiac surgery or to eliminate blood coagulation arising from us of medical implementation. Further antibodies are disclosed to be employed in in vivo diagnostic methods including in vivo diagnostic imaging of native human TF.
WO04/094475 provides antibodies capable of binding to human tissue factor, which do not inhibit factor mediated blood coagulation compared to a normal plasma control. Human antibodies are not described. It is alleged that the antibody may be used for treatment of cancer.
WO03/093422 relates to antibodies that bind with greater affinity to the TF:VIIa complex than to TF alone. Use of the antibodies as anticoagulant in the treatment of certain diseases, such as sepsis, disseminated intravascular coagulation, ischemic stroke, thrombosis, acute coronary syndromes and coagulopathy in advanced cancer is proposed.
WO01/27079 discloses compositions and methods for inhibiting abnormal cell proliferation, particularly endothelial cell proliferation, such as cancer, abnormal development of embryos, malfunctioning of immune responses, as well as angiogenesis related to neovascularization and tumor growth. Many active substances, including antibodies, are proposed, but no specific antibodies are disclosed.
WO03/037361 relates to us of TF agonist or antagonist for treatment related to apoptosis.
WO03/029295 relates to isolated human antibodies that immunoreact with human TF to inhibit the binding of coagulation factor VIIa. However, the application does not disclose a single example of an antibody having these properties.
A number of monoclonal antibody therapies are approved to treat different tumor types, including e.g. bevacizumab (Avastin®), cetuximab (Erbitux®), panitumumab (Vectibix™) and trastuzumab (Herceptin®).